A light-sensitive material containing silver halide, a reducing agent and a polymerizable compound is disclosed in Japanese Patent Publications No. 45(1970)-11149 (corresponding to U.S. Pat. No. 3,697,275), No. 47(1972)-20741 and No. 49(1974)-10697 (corresponding to U.S. Pat. No. 3,746,542). The light-sensitive material is used in an image-forming method comprising polymerizing a polymerizable compound by action of a reducing agent within the area where a latent image of silver halide has been formed. The method disclosed in the publications employs a wet development process.
An improved image-forming method employing a dry process has also been proposed in Japanese Patent Provisional Publications No. 61(1986)-69062 and No. 61(1986)-73145 (the contents of both publications are described in U.S. Pat. No. 4,629,676 and European Patent Provisional Publication No. 0174634A). In the method, a recording material (light-sensitive material) comprising a support and a light-sensitive layer provided thereon which contains a light-sensitive silver salt (silver halide), a reducing agent, a cross-linkable compound (a polymerizable compound), a binder and a color image forming substance is imagewise exposed to light to form a latent image, and then heated to polymerize the polymerizable compound within the area where a latent image of the silver halide has been formed.
There is further proposed another image-forming method in which the polymerizable compound is polymerized within the area where a latent image of the silver halide has not been formed. This method is described in Japanese Patent Provisional Publication No. 61(1986)-243449 (corresponding to European Patent Provisional Publication No. 0202490A). In the method, the polymerization of the polymerizable compound is inhibited within the area where a latent image of the silver halide has been formed, and the polymerization of the polymerizable compound is accelerated within the other area (i.e., the area where the latent image has not been formed).
The image-forming method using the above-mentioned light-sensitive material generally comprises the steps of imagewise forming a polymer image on the light-sensitive material, pressing the light-sensitive material on an image-receiving material having an image-receiving layer to transfer the unpolymerized polymerizable compound to the image-receiving material so as to obtain a transferred image on the image-receiving material. In this method, the silver halide and the polymerizable compound in the light-sensitive material are preferably contained in microcapsules (i.e., light-sensitive microcapsules). The light-sensitive microcapsules are described in Japanese Patent Provisional Publications No. 61(1986)-275742 and No. 61(1986)-278849 (contents of both publications are described in European Patent Provisional Publication No. 0203613A). Employing the light-sensitive microcapsules, an image of high quality can be obtained.
As the shell material of the microcapsules, a variety of resins have been proposed, for example, in Japanese Patent Provisional Publications No. 62(1987)-209438 (corresponding to U.S. Pat. No. 4,888,265), 62(1987)-209439 (corresponding to U.S. Pat. No. 4,833,062) and No. 63(1988)-269146 (corresponding to U.S. Pat. No. 4,880,721). Further, in the preparation of microcapsules, a specific protective colloid (a mixture of pectin and a styrenesulfonic acid polymer) can be used, as is described in Japanese Patent Provisional Publication No. 63(1988)-121837 (corresponding to U.S. Pat. No. 4,842,978).
On the other hand, the development and the polymerization reactions in the above-mentioned image-forming methods smoothly proceed under alkaline conditions. Accordingly, the light-sensitive layer of the light-sensitive material preferably contains a base or a base precursor as an image forming accelerator. A light-sensitive material containing a base or a base precursor in the light-sensitive layer is described in Japanese Patent Provisional Publication No. 62(1987)-264041 (corresponding to European Patent Provisional Publication No. 0219087A).
Furthermore, a light-sensitive material in which a base precursor is contained in the light-sensitive microcapsules is described in Japanese Patent Provisional Publication No. 64(1989)-32251 (corresponding to European Patent Provisional Publication No. 0301539A and copending U.S. patent application Ser. No. 07/225,456, filed 07/28/88 now, U.S. Pat. No. 4,939,064. In the case that the base or base precursor is contained in the light-sensitive microcapsules, the image forming reaction is directly and effectively accelerated by the base or base precursor. According to the invention of Japanese Patent Provisional Publication No. 64(1989)-32251, the solid particles of the base precursor are directly dispersed in the polymerizable compound.
The light-sensitive material proposed in Japanese Patent Provisional Publication No. 64(1989)-32251 is highly advantageous, but further improvement is desired. For example, the base precursor is not completely kept within a core material (i.e., oily liquid containing the polymerizable compound) of the microcapsules in preparation of the microcapsules. Further, the base precursor partially moves from the core material to an aqueous medium outside of the microcapsules. The base precursor in the aqueous medium inhibits the encapsulation reaction. Therefore, the resulting microcapsules have a reduced denseness of the microcapsule shell, and the core material is not kept within the microcapsules. As a result, the core material oozes out of the microcapsule at the development process, and the maximum density in the image portion is thus decreased (namely, the amount of the unpolymerized polymerizable compound transferred from the microcapsules to an image-receiving material is decreased). Further, the minimum density in the background portion is increased (namely, the white background is slightly colored). The oozed polymerizable compound is not sufficiently polymerized because the compound is exposed to air, which functions as a polymerization inhibitor.